Electronic timing control system



G. E. UNDY ELECTRONIC TIMING CONTROL SYSTEM 2 Sheets-Sheet l Filed June2, 1944 Y Zl/ )lap Oct. 19, 194.8. G. E. UNDY 2,451,997

ELECTRONIC TIMING CONTROL SYSTEM Patented ct. 19, 1948 ELECTRONICTI'MING CONTROL SYSTEM Gustav E. Undy, Detroit, Mich.,v assigner, bymesne` assignments, to Weltronic Company,A Oakland; County, Mich., acorporation of Mlchigall Appication June 2, 1944, Serial'Not 538,407'

(Cl. Z50- 27) 11- Claims. 1

Thel present invention relates to timing control systems, and, in itsdisclosed embodiments, pro-l videsi-mproved and simpliiied controlsystems for resistance welding systems ofthe pulsation type.

TheV 4princi-pal objects of the present invention are to. provideimproved systems of the above, genera-ily indicated' type, which aresimple in construction, economical of manufacture, and. eilicient andreliable. in operation to. provide such systems which may becharacterized as providing for the delivery of current, from anassociated source, tot a' work-t circuit, duringV each 0f apredetermined number-of periods, andv asA further embodying meansr foradjustably determining the number` o1". such periods; toy provide suchan arrangement' wherein the= number of suchperiods is determined inaccordance with the relative capacities of two: or morel energy storagedevices, preferably condensers;` to provideV such systems wherein -foreachsuch period, a part ofthe energy lis withdrawn from one storagedevice, the succession being terminated 'when` the summation of such.parts reaches a. predetermined proportion ot thev total energyoriginallystored in the device; to providey such arrangements wherein the part Vofsuch energy which is withdrawn for each suchv period is the amount ofenergayrequired to charge a companion energy storage device to apredetermined potential; and. to provide such arrangements wherein the.storage devices from which the energy isY withdrawn, as aforesaid", iscoupled to an. electric valve in such:4 relation as to control theconductivity thereof.

With the above as `Well as otherk objects in view, which appear in'. thetollowing'l description and in the appended. claims, preferred,illustrative em- Iboidiments of the invention are shown in the1 accompan-ying dra-Wings,v throughout the several views lot which;corresponding reference charactersare usedV .to Vdesignate correspondingparts; and in. which l. is -a diagrammatic view of control circuitsembodying thel invention;

Fig. 2 is a diagrammatic representation of certainottheelectromagneticrelays utilized in the systems of Figs. l andv 3,and showingk the mechanical relationship between the coils and contacts,which are'sh-ownf separated from each other inFigs. l and 3; and.

Fig. 3: is a diagrammatic illustration ot the. control circuits forminga modification ofv the invention.

, It will be appreciated from a. complete under:- stand-ing of thepresent invention that, in a genericlsense, mprovementsthereof may be'used in electrical. control systems adapted for widely differingpurposes and employing widely differing circuit relationships, Thepresent systems represent preferred embodiments adapted for usey inresistance welding control systems of the pulsation type, and areYdisclosed herein in an illustrative but not in a limiting sense.

In certain of its aspects the improvements of' the present inventionhave to do primarily With the provision of counting or integrati-ngcircuits which serve to control 0r determine the number of successivecontrol operations which resul-t from an actuation of an initiatingIcontrol member. In the system of Fig. 1 .this apparatus is embodied inaso-called non-synchronous, pulsation control system. In Fig. 3.,. thesystem is embodied in: a. pulsation control system which incorporates asynchronous timing feature. In each instance, current is delivered from.an associated source to a work circuit, illustrated as a Weldingcircuit, in a suc-cession of on periods, and successive on periods[being spaced. apart by an off period, each on period and each 05"period comprising either an approximately or a precisely determinedlnumber of half cycles of the associated source. The counting, orintegrating, apparatus serves to determine the number of periods in eachsuch succession.

Referring. to Fig. 1, the primary winding of the welding transformer WTis arranged for connection across the line conductors Ll and L2, inseries With av pair of conventionally and reversely connected electricvalves Ml and M2. The secondary winding of the Welding transformer WT isdirectly connected in the Work circuit, illustrated as aresistancewelding circuit, employing usual electrodes l0. and IZ.Electric valves Ml and M2 may be of any suitable, controlled type,such,V for example, as the gas lled` mercury pool discontinuous controlre ctiers sold commercially under the trade name Ignitron.. As will beunderstood., these valves are normally non-conductive, but may berendered conductive during half cycles, during which the anodes athereof are positive with respect to their cathod'es c, by applying anigniting potential between the igniters ithereof and such cathodes c.When so rendered conductive, the valves' remain conductive for thebalance of the hal-f cycle of current ow then in progress. The

valveslMl and M2 are rendered conductive during each half cycle of eachon periodand are maintained non-conductive during the intervenin oirperiods.

The control apparatusvfor` controlling the conductivity at main valvesMl and M2 comprises vscription of the operation thereof.

3 a series of electric valves VI, V2, V3 and V4 and associatedelectromagnetic control relays CRI, CR2, CRS, OR4 and FR. The mechanicalrelation between the contacts of the just-mentioned relays is shown inFig. 2, it being understood that the contacts of these relays occupy thepositions shown in Fig. 1 when the coils thereof are deenergzed and moveto and remain in, an oppo#l site position when, and so long as, suchcoils are I energized. Valves VI through V4 may be of any usual type butare preferably usuall three-element evacuated valves of the continuouscontrol type.

cathodes, and in which the grids thereof are neutral or positive withrespect to suchoathodes; .l

4 between the electrodes I and I2 so as to clamp the work Wtherebetween.

Upon being energized, transformer TI applies a potential across valve VIand control relay CRI. Under the conditions stated, the grid of valve VIis neutral with respect to its cathode and this valve is consequently,in a conductive con* dition. Thus, transformer TI is able to passcurrent through valve VI and energize control relay CRI.

.Upon being energized, control relay CRI closes its contact CRIa, whichaction serves only to As will be understood, these valves areV`conductive during half cycles, in which thev anodes thereof are positivewith respect to their'u` To simplify the drawings, the circuits, throughwhich heating current is applied to the heatingi elements of valves VIthrough V4, have been omitted, such circuits being represented by the'reference characters :I:.

The initiation of a welding cycle is illustrated as being under thecontrol of a pilot switch P, which, will be understood, may be eithermanen ually or automatically controlled.

It is believed that thev remaining details of the system lmay best beunderstood from a de- Assuming that it -is desired to condition thesystem to make a weld,l the illustrative disconnect switches LSI and LSZmay be closed, which action connects' line conductors LI and L2 to thesource of power, which may be an alternating current source ofcommercial frequency. The energization of lin'e conductors LI and L2completes obvious energizing circuits for the primary windings ofcontrol transformers T5 and T9, associated withA the grids of valves V2Vand V4. Inresponse to this action, transformer T5 applies a'negativebias to the grid of valve V2 rendering the latter nonconductive and alsocharges up an associated control condenser I4. The energization oftransformer T9 applies a negative bias to the grid of valve V4 and alsocharges up a' pair of counting-condensers I6 and' I8,whicl'l'cooperate,4as described below, to determine the number of periods during whichcurrent is supplied to the' welding circuit in response to asingle'actuation of the pilot switch P. It will be noted that con-vdensers I6` and I8 are directly connectedV in parallel through anormally closed contact 0R31) of control relay CR3 and are lthuscharged' to the'same potential when the system'is in readil ness to makea weld. l

The energization ofl line conductors LI-LZ also applies a potentialVacross vthe primary winding of the welding transformer and across theparallel connected main valves MI and M2. Such action is without effect,however, since valves MI and 'M2 are normally non-conductive,`` and'Vremain` so unless-and until the aforementioned igniting impulses areapplied thereto.

, Assuming it isk desired to make a we,ld,.and assuming `further thatthe -work W has been properlypositioned between fthe electrodes `Il] andI2, the pilot switch P may be closed. `Closure of switch P completesobvious .energizing circuits, in parallel with each other, for thesolenoid operated valve EV and thel primary windings of transformers TI,T3 and T4. Valve-EV-may. be of a usual type, which, upon being energizedactuates associated conventional apparatus (not shown) and therebycauses a relative movement provide a holding circuit in parallel withthe pilot switch P, which may, consequently, be returned to the openposition without effect upon the welding operation now in progress.

Upon being energized, transformer T4 opposes and overcomes the biasingpotential of the originally energized transformer T5, enabling theenergy stored in the condenser I4 to start discharging through the localcircuit, including resistor 2i).Y At the expiration of a dischargeperiod, proportioned to allow time for the abovementioned clampingmovements of the electrodes It and I2, the grid of valve V2 attains apotential relative to the cathode of this valve at which this valve isconductive. At this time, the now energized transformer T3 is enabiledto pass' current to and through control relay CR2 and energize thelatter, thereby initiating the flow of welding current.

. More particularly, upon being energized, relay CRZ kcloses its contactCRZa and opens its contact CRZb. The opening of contact CRZb interruptsthe originally complete energizing circuit for transformer T9, whichaction is without immediate effect, except that it interrupts the sourceof charging current for the counting condensers I6 and I8. Thesecondensers remain effective, however, to maintain a negative bias on thegrid of valve V4, thereby maintaining the latter in a non-conductivecondition.

Closure of contact CRZa completes obvious energizing circuits inparallel for the primary windings of transformers T6 and T8, the circuitfor transformer T6 being subject to the now closed contact` 0R41) ofcontrol relay CR4.

Upon being energized, transformer T6 is enabled to pass current throughthe normally conductive valve V3 and energize control relay CRS. Uponbeing energized, control relay CRS closes its contact CR3a, opens itslcontact ORSI) and closes its contact CRSc, the opening of contact CR3bbeing preferably timed to take place slightly ahead of theclosure ofcontact 0R30.

Closure of contact CR3a completes obvious energizing circuits inparallel for the coil of the firing relay FR and for the primary windingof control transformer T'I. The energization of ring relay FR causesclosure of its contact FRa. Contact FRa is connected between theigniters of mainvalves MI and'MZ in the mannerdescribed in the Slepianet al. Patent No. 2,165,911, and, in accordance with the description inthis patent, such closure -results inr applying an igniting impulse tothat one of the main valves MI and M2 whose 'anode is positive duringthe half cycle in question. So long'as contact FRa remains closed also,the igniting impulses are applied to the respective valves MI and M2,during successive half cycles. Closure vof contact FRa thus initiatesthe flow of welding current to the welding transformer WT and to theassociated welding circuit.

.Upon being energized, transformer T1 applies anegative bias` to the`'grid vof valve V3,.whieh ac'- s. tionlrenders thisvalVe'non-conductive and also charges up an associated timing condenser22. The blocking of valve V3 interrupts the flow of energizing currentto thev coil of control relay CR3, enabling the energy stored in theassociated timing condenser 24 to discharge therethroughand-maintainrelay CR3 energized during the rst on period, the length whereof is thusdetermined by the relative characteristics of relayk CRI. and condenser24. At the expiration oi` a timing period determined by the adjustmentofv condenser 24y control relay CR3 resumes the de-energized position.

Morev particularly, when control relay CR3 resumes the de-energizedposition, it opens its contact;y CR3a and restores contacts CRS?) andCR3c to the illustratedv positions, the opening of contact CR3c beingpreferably timed to lslightly lead the closure of contact CRSb. Theopening of C1'-\.3a'k de-energizes the ring relay FR and alsode-energizes the transformer T1,

The de-energization of ring relay FR causes its contact FRa to open.This action is without eiect on the conductivity of the main valve thenpassingv current, but prevents the ignition of the other main valve atthe beginning of the next succeeding half cycle. The opening of contactFRA is thus effective at the expiration of the halfv cycle then inprogress to interrupt the flow of welding current to the weldingcircuit.

The de-energization of transformer TI enables-the energy stored incondenser 22 to start discharging through the local circuit, includingresistor 26, and at the expiration of an adjustable period, brings thegrid of valve V3 to a potential at which valve V3 is conductive. Thetiming period afforded by condenser 22 determines length of the oifperiods which intervene between the on periods.

More particularly, when valve V3 is again rendered conductive by thetiming out `of condenser 2.2', transformer T6 is effective to againenergize control relay CR3 in the previously described manner. Whenenergized, control relay CR3 functions as before to energize the iiringrelay FR (thereby initiating another iiow of Welding current to the weldcircuit) and also re-energizing transformer T1. The latter action againblocks valve V3 and enables condenser 24 to determine the lengthof theperiod of welding current flow. So long as transformer T6 is energizedaccordingly, control relay CRS pulsates between an energized conditionand a de-energized condition. So long as control relay CR3 is energized,current flows to the welding circuit, and so long as it is deenergized,current. flow to the Welding circuit is prevented, As will beunderstood, the settings for condensers 22 and 24 may be adjusted toprovide a widely Variable number of half cycles in each such on periodand in each such o period.

Considering now the action of contacts CR3b andY CR3c, it will beunderstood that at the beginning ofv and during each on period, contactCR3b is open and contact CR3c is closed. The opening of contact CR3btemporarily isolates condenser IB from condenser I6, and the'closure ofcontact 0R30 completes a low resistance discharge path for condenser I8.Upon completion of this discharge circuit, the energy in condenser IBisv promptly dissipated.

At. the expiration of the rst on period, contacts CR3b and 0R30 resumethe illustrated positions. Such action interrupts the just-traceddischarge circuit; for condenser I8 and completes Cil 6, a circuitthrough which energy is enabled to discharge from condenser IG'intocondenser I8. In the usual case in which it is desired to pass weldingcurrent to the load circuit during each of a plurality of periods,condenser I8 is adjusted to have a considerably lower capacity thancondenser IG, so that such discharge thereof, sufficient to again bringcondensers I5 and I8 to theV samecharged potential, withdraws fromcondenser I 6 only a portion of the energy stored therein. Suchwithdrawal lowers the potential of the condenser I6 and correspondinglyreduces the negative bias on the grid of valve V4, but, in the'usualcase, such reduction in the negative bias of the grid of valve V4 is notsufiicient to render this valve conductive. At the conclusion of the offperiod in question, control relay CRB is again energized, as describedabove, which action, at contacts-CRM, initiates the second period ofwelding current iiow. Such .re-energization, at contact CRSb, isolatescondenser I8 from condenser IG, and, at contact 0R30 again completes thedischarge circuit for condenser I8 AThe portion of the charge ofcondenser I6 which is transferred to condenser I8 at the end of the rston" period is, consequently, dissipated to ground at the beginning ofthe second on period.

A-t the end of the second on period, relay CRS is again de-energized, asdescribed below, andrestores contacts CRS!) vand CRSc to the illustratedpositions. These actions interrupt the discharge circuit for condenser I8 and enable a second portion of the charge of condenser I6 to betransferred to condenser EB. Such second transfer again reduces thepotential of condenser I6, but assuming that more than two on" periodsare desired, such reduction does not entirelyl eliminate the negativebias on valve V4.

Similar operations occur at the end of the second and succeeding olfperiods and at the beginning of the third and succeeding on periods.

At the expiration of the last on period of the series, the transfer of apart of the residual energy in condenser I6 to condenser I8 brings thepotential of condenser I6 to such a low value as to eliminate theeiective bias on thegrid of valve V4. The latter action renders valve V4conductive at the expiration of such last on period.

When valve V4 is rendered conductive, the still energized transformer T8is enabled tc pass current therethrough and energize relay CR-i, whichthereupon closes its contact CRlIa and opensits CRM). The latter actionde-energizes transformer T6 and thereby effectively prevents areenergization of control relay CRS. The closure of contact CR4acompletes an energizing circuit for the primary winding of transformerT2, associated with valve VI. Upon being energized, transformer T2applies a negative bias to the grid of valve VI, thereby rendering thelatter nonconductive.

WhenY valve VI is rendered non-conductive, control relay CRI is heldenergized for a short period by the energy stored in its associatedcondenser 3i). At the expiration of this short period, knownconventionally as a cool period, control relay CRI resumes theillustrated position, opening its contact CRIa. The opening of contactCRIa interrupts the initially `traced maintaining circuits in parallelwith the pilot switch P and interrupts the circuits for the electrodevalve EV and for transformers T3 and T4. As will be obvious, thede-energization of the latter two transformers interrupts the supply ofthe energizing' current for control relay CR2 and enables,

transformer T5 to again apply a blocking bias to the grid of valve V2.Upon being de-energized, control relay CRZa interrupts the initialenergizing circuit for transformers T6 and T8, it being noted that underthe conditions stated, the circuit for transformer T6 is stillinterrupted at contact CRdb. l

The de-energizing of transformer T8 interrupts the supply of energizingcurrent for the coil of relay CRA, thereby restoring this relay lto thedeenergized position, opening its contact CRIa and reclosing its contactCRllb. The reclosure of con tact CRA b is without eiect, since contactCR2a is now open, but the re-opening of contact CR4a de-energizestransformer T2, thereby again con-l ditioning valve VI for operation.

The resetting operation described above is completed by the reclosure ofcontact R21), which again energizes transformer T9, thereby re-applyinga blocking bias to the current of va1ve V4 and again rechargingcondensers I6 and I8 to the full potential.

It will be noted that the coils of relays CR2 and CR4 are provided withfiltering condensers 32 and 34, which have sufficient capacity tomaintain these relays energized during a half cycle, which immediatelyfollows a half cycle in which the associated valves are conductive.

From the foregoing, it will be appreciated that a new welding cycle,duplicating the described cycle, may be initiated by a momentaryreclosure of the pilot switch P. In such cycle, by way of a summary,control relay CR3 and its associated timing elements, includingcondensers 24 and '22, determine the lengths of the successive on andoff periods; during each on period current is passed to the weldingcircuit, and durinar each off period such current flow is prevented; andcondensers I6 and I8 cooperate to control the conductivity of valve V4and serve to determine the number of on periods in the series. It willbe noted that condensers I6 and I8 affect this control in accordancewith their relative capacities, and in accordance with the rates atwhich the energy is dissipated therefrom, and thus provide for a cycleincluding one or a predetermined plurality of on periods.

The system shown in Fig. 3 is generically the same as the systemdescribed above, with the exception that in this instance, a synchronoustimer l) is interposed between the impulsing relay CRS (whichcorresponds in other respects to the previously described relay CRS) andthe ffing circuits of lthe main rectifiers MI and M2. The synchronoustimer 5B may be of any suitable conventional type arranged, wheninitially energized, to provide an on period of a precisely determinednumber of half cycles. Such a suitable timer is described and claimed inthe copendingI application of the present applicant, Serial No. 450,483,filed July 10, 1942, now United States Patent 2,420,919, issued May 20,1947. More particularly, the starting switch, designated 26 in thecopending application, may correspond to the contact designation CR3'din Fig, 3 of the present application; and valves MI, M2, V5 and VG'ofthe present application may correspond to valves RI, R2, VI and V2 ofthe copending application.

In Fig. 3, accordingly, the length of each on period is determined bythe synchronous timer 50. As before, however, the lentgh of each offperiod is again determined by condenser 22, associated with the gridcircuit of va1ve V3. As before,

the overall number of periods is determined byA the counting condensersI6 and I8 which Afunction to control the conductivity of the valve V4.In

this case, the relay which is connected in the anode circuit of valve V4is designated CRG instead of CRA.

Considering the operation of Fig. 3 in more detail, the operations whichresult from the closure of line Witches LSI and Ls2 duplicate theoperations described with reference to'Fig. l. Also, the operationswhich result from the closure of the pilot switchP duplicate thepreviously described operations in so far as concerns the electr-odevalve EV and control relays CRI, CR2 and CRS.

It will be recalled that the energization of electrodev valve EVI causesthe electrodes to move to clamping engagement with the work, and thatrelay CR2 interposes a delay which permits the completion of suchelectrode movement before the impulsing relay CRB is energized. Theremaining. operations which take place in the sys- Closure of contactCRSa prepares a circuit for an auxiliary control relay (3R-5, andclosure of contact CRSIJ energizes the synchronous timer 50 in themanner described, for examplein the aforesaid copending application.Upon being energized, vtimer 50 serves to apply, at precisely determinedpoints, in a predetermined number'of successive half cycles, ignitingpotentials'between the grids and cathodes of the auxiliary ring valvesV5and V6. Valves V5 and V6 may be, and preferably are, conventionalgas-lled, discontinuous control-type rectiers and are conventionallysituated between the anodes and the ig;- niters or" the respective mainrectifiers MI and M2. As it will be understood, each time valve V'5 issupplied with an igniting impulse, which overcomes the bias voltage ofits associated battery 5l), such valve becomes conductive and applies anigniting potential between the igniter and the cathode of thecorresponding main rectifier MI. Similar comments apply to valve V5.

The energization ofthe synchroncustimer 50 thus initiates the deliveryof Welding current from the source to the welding circuit. In accordancewith conventional practices, timer 50 not only determines the proportionof each half cycle throughout which current flows, but also determinesthe number of half cycles in a particular on period. At the expirationof the on period in question, timer 50 operates to prevent furtherdelivery of igniting impulses to valves V5 and V6 Yuntil such time asthe timer 50 is reset by the opening of contact CR3d and is againactuated by a reclosure of such contact.`Vv

At the beginning of the just-mentioned onl period, the potentialimpressed across the primary of the welding transformer WT is alsoapplied across a relay CRA', which is connected in the anode circuit ofa conventional rectier V'I. A condenser 52 serves to maintain a supplyof energizing current to relay CR4 during each half cycle, which followsa half cycle in which 'valve Vl conducts current. At the beginning ofthe on period in question, accordingly, relay CR4 is energized andremains so until the end of the on period.

Energization of relay CR4 causes closure of `the grid of valve V3.

`its contact CRM) :andthe openingof its contact `.CRNCL Closure of theformer contact completes the originally vprepared circuit for relay CRS,

=whichthereupon moves to the energized position, vclosing its contactsCRSa and CRSb. Closure of `the latter contact completes a maintainingcir- .cuit for relay CRS, which circuit is subject to contact CR3a.Closure of contact vCRais without effect, since contact CRa is now open.

At the end of the on period in question, the interruption of the supplyof current to the Welding transformer also interrupts the supply ofcurrent torelay'CR/l'a, which thereupon resumes the illustratedposition, opening its contact CRllb and reclosing its contact CRa. Thereopening of the former contact is without immediate effect, but thercclosure of Contact CRAa completes an energizing circuit fortransformer T1, associated with Upon being energized, transformer Tlapplies a blocking potential to the grid of valve VE and renders thelatter nonconductive. In this case, condenser 24', connected in parallelwith the coil of relay CRB', is proportioned to hold this relayenergized for not more than a half cycle. Consequently, the block'- ingof valve .V 3 .results in the virtually immediate de-energization of`relay CRS', Which thereupon restores all of its contacts totheillustrated positions.

The re-opening of contact CRBd effects the previously-mentionedresetting of the synchronous timer 50 and conditions it for thesucceeding on period. The re-opening of Contact CRSa de-enelgizes relayCR5, whichthereupon resumes .the `illustrated position, interrupting itsown maintaining circuit, and (at contact CRSa), deenergizing transformerT7. .Thede-'energization oftransformer T1 enables thev energystored incondenser'z to start discharging-as before and at theexpiration of suchperiod,*determinedA by condenser 22, valve V3 again becomes conductive.VlhenvalveVB is renderedconductive it initiates the succeeding on periodin the manner .described above. So long, therefore, as transformer T6remains energized, relay CR3 is impulsed between energized andde-energized positions, each energized period being an on period (thelength whereof is determined by timer 50), and each deenergized periodbeing an off period (the length whereof is determined by condenser 22).

As in connection with Fig. 1, the openingr of contact CRZb, at thebeginning of the first on period, isolates the counting condensers I6and I8 from the source. At the beginning of each on period, the openingof contact CRSb and the closure of contact CR3c enables a promptdischarge of condenser I8. The retransfer of these contacts at the endof each on period enables a portion of the charge of condenser I'G to betransferred to condenser I 8. A predetermined number of such transferslowers the potential of condenser I8 to such a value as to render valveV4 conductive, which action enables transformer T8 to energize relayCRi. Upon being energized, relay CRB terminates the welding operationand effects a complete resetting of the system, in the manner describedin connection with the energization of relay CRI! in Fig. l.

Although only two specic embodiments of the invention have beendisclosed in detail, it is believed to be obvious that furthermodifications of the invention may be made without departing from thespirit and scope thereof.

What is claimed is:

1. In a timing control system for controlling tthe'delivery'of currentfrom a source of current to' a `work circuit duringV each Vcfaplurality-of spaced periods of time, the combination of means forcausinga said delivery of current during each period and .to kprevent aflow during the intervening spaces of time; translating means actuablefor limiting the :number of vsuch periods, means including a pair ofenergy storage devices, means enabling an energytransfer from onesaiddevice tothe other, and-means operable lwhen'a.predetermined amount ofsaid len- .ergy has been transferred for actuating said translatingmeans. l

2. Apparatus asset forth in claim 1 wherein a part ofthe energy of onesaiddevice is transferred to the other at theconclusion of each saidperiod."

3; Apparatusas set forthin claim 1 wherein a part of the energy of `onesaid device is transferred tothe other at theconclusion of each saidperiod, and wherein the part so transferred is discharged from the otherprior to the beginning ofthe next period.

y4. Apparatus as set forth in claim l wherein said translating meansincludes an electric valve having a control grid and wherein saiddevices are coupled to said grid '5.`Apparatus as set yforth in claim 1wherein a part of the energy of one said device is trans! ferred to theother in response to the operation of said first-mentioned means.

6. In an electrical control system, an electric valve 'having principalelectrodes and a control electrode, and meansfor controllingtheconductivity of said valve including a pair of condensers at least onewhereof is adapted to receive charging current 'from an associatedsource and is coupled between said control electrode and one of saidprincipal electrodes, and means for incrementally transferring thecharge of said one condenser to the other condenser, whereby to controlthe conductivity of said Valve.

7. The system ofclaim 6 wherein lsaid means includes means fordischarging each such increment from said second condenser before asucceeding increment is transferred thereto.

8. In a timing control system for controlling the delivery of currentfrom a source of current to a Work circuit during a predeterminedinterval, means for initiating a said flow of current, timing means forlimiting the length of said period, said timing means comprisingtranslating means, means including a pair of energy storage devices,means enabling an energy transfer from one said device to the other, andmeans operable when a predetermined amount of said energy has beentransferred for actuating said translating means.

9. In anelectrical control system, a circuit adapted to supply a loadthe energization whereof isv to be controlled in accordance with apredetermined pattern, a rst operating means for controlling saidcircuit, a first regulating means for controlling the time period duringwhich said operating means is permitted to maintain said circuit in afirst condition, a second regulating means for controlling the timeperiod during which said operating means is permitted to maintain saidcircuit in a second condition, circuit means interconnecting saidregulating means whereby said regulating means are alternately renderedeffective to provide for alternately maintaining said load circuit insaid rst and second conditions, a network including a pair of condensersof differing charge capacities for determining 'the time' period inwhich said load '.circuit is maintained in said conditions, and a secondcircuit-controlling means actuated by said inter-connecting circuitmeans for controlling the interchange of energy between said condensers,v

10. In an electrical control system, 'a circuit adapted to supply a loadthe energization whereof is to be controlled in accordance with apredetermined pattern, a rst operating means for controlling saidcircuit, a first regulating means for controlling the time period duringwhich said operating means is permitted to maintain said circuit in afirst condition, a second regulating means for controlling the timeyperiod during which said operating means is permitted to maintain saidcircuit in a second condition, circuit means interconnecting saidregulating means whereby s-aid regulating'means are alternately renderedeffective to provide for alternately maintaining said load circuit insaid rst and said second conditions, a network including Ia pair ofcondensers of differing charge capacities for determining the timeperiod in which said load circuit is maintained in said conditions, asecond circuitcontrolling means actuated by said interconnecting circuitmeans for permitting a transfer of energy from one of said pair ofcondensers to a second of said pair of condensers, and a third circuitmeans actuated by said interconnecting 3 circuit means for dischargingsaid second condenser during the time interval between the peri- .duringwhich the other of said pair of currentcontrolling means is in onecontrolling condition, said one current-controlling means acting uponactuation to a second controlling condition to place said othercurrent-controlling means in its said one controlling condition, saidother currentcontrolling means acting upon actuation to its secondcurrent-controlling condition to place said one current-controllingmeans in its said one controlling condition, means actuated by saidother current-controlling means to control the actuation of saidoperating means in accordance with the actuation of said othercurrent-controlling means whereby the ow of energy through said loadcircuit is controlled, a second network comprising a pair of condensersof diiering charge capacities for determining the time period ofoperation of said iirst network, means for initially charging one ofsaid condensers, means operable periodically to provide a transfer ofcharge from said one condenser to the other of said condensers, means todischarge said other condenser during the time interval between saidcharge transfers, Iand means responsive to a predetermined minimumcharge of said one condenser to render said rst network ineffective.

GUSTAV E. UNDY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNTED STATES PATENTS Number Name Date 2,193,850 Andrieu et al Mar. 19,1940 Y 2,232,541 Levoy, Jr. Feb. 18, 1941 2,233,810 Dawson Mar. 4, 19412,270,799 Gulliksen Jan. 20, 1942 2,303,453 Gulliksen Dec. 1, 19422,329,090 Smith et al Sept. 7, 1943 2,340,077 PearsonI et al Jan. 25,1944 2,366,038 Livingston Dec. 26, 1944 vr2,370,178 Livingston Feb. 27,1945

